Map Operating Mode (enum) to CPU Frequency

Level: Easy
Concepts: Variables & Data Types

Scenario

An embedded controller runs at different CPU frequencies depending on an operating mode. In power‑save mode, frequencies should be reduced by half.

Problem Statement

Implement a function that maps an operating mode (enumerated) to its corresponding CPU frequency in MHz, optionally applying a power‑save reduction. Invalid enum values must be reported as an error.

Requirements

• Define the enumeration- Mode { MODE_SLEEP, MODE_IDLE, MODE_RUN, MODE_BOOST }

• Base frequencies (example design):

  • MODE_SLEEP → 0 MHz
  • MODE_IDLE → 24 MHz
  • MODE_RUN → 48 MHz
  • MODE_BOOST → 96 MHz

• If power_save == true, return half the base frequency (integer division).

• For invalid enum values, return ‑1.

• MODE_SLEEP must always return 0 MHz, even when power_save is true.

Function Details

Name: mode_to_cpu_mhz

Arguments:

• enum Mode mode – operating mode to be mapped.
• bool power_save – flag indicating whether to halve the base frequency.

Return Value:

• int – CPU frequency in MHz; -1 for an invalid mode.

Description:
Validate that mode is one of the defined enumeration values. Retrieve the corresponding base frequency, apply the power‑save reduction when requested (except for MODE_SLEEP), and return the result. If the mode is not recognized, return -1.

Solution Approach

1. Validate the mode value; if it is outside the range of the defined enum, return -1.
2. Map the enum to its base frequency using a switch (or lookup table).
3. If mode == MODE_SLEEP, set frequency to 0.
4. Otherwise, if power_save is true, divide the base frequency by 2 using integer division.
5. Return the final frequency.

Tasks to Perform

1. Write the enum Mode definition.
2. Implement mode_to_cpu_mhz following the solution steps.
3. Verify that the function works for all valid modes, respects the power‑save flag, and correctly handles invalid enum values.
4. Create unit tests covering the cases listed below.

Test Cases

| 6 | mode = MODE_SLEEP, power_save = true | 0 | Remains zero even with power‑save |